Method for recovering and producing potassium salts



United States Patent 3,429,657 METHOD FOR RECOVERING AND PRODUCINGPOTASSIUM SALTS DArcy R. George, James M. Riley, and J. Richard Ross,Salt Lake City, Utah, assignors to the United States of America asrepresented by the Secretary of the Interior N0 Drawing. Filed Sept. 2,1966, Ser. No. 577,085 US. Cl. 23-63 9 Claims Int. Cl. C01d 3/14, /00,9/02 ABSTRACT OF THE DISCLOSURE A potassium-bearing brine is contactedwith NaClO to precipitate KClO, which is then separated and formed intosolution. The potassium in the solution ion exchanged with sodium, afterwhich the resultant free p0- tassinm is combined with chloride, sulfate,nitrate or carbonate ion.

This invention relates to the recovery and production of potassium saltsfrom solutions.

In the processing of natural brines or brines prepared from mineralsalts containing NaCl, KCl and MgCl the potassium may be readilyrecovered as KCl substant1ally free of sodium or magnesium by simplefractional crystallization, including solar evaporation. However, ifsuch brines contain sulfate, which is commonly present as Na SO thefractional crystallization procedures become complex, and at highsulfate concentrations the potassium can be recovered only as relativelyvalueless double sulfates of sodium or magnesium. If such brines couldbe desulfated, fractional crystallization or other techniques could beeasily applied to the residue chlorides. However, the various proposeddesulfating methods have been either ineffective or economicallyimpractical.

It has now been discovered that potassium salts can be economicallyrecovered and produced from potassiumbearing brines and other complexsolutions by (1) precipitating potassium as KClO, by the addition ofNaClO to a brine, (2) recovering the precipitated KClO (3) forming asolution of the KClO (4) contacting the KClO solution with an ionexchange resin to separate potassium ion from perchlorate ion, and (5)combining the potassium ion with a selected anion to form a solutionfrom which a desired potassium salt can be recovered by conventionalevaporation techniques.

It is therefore an object of the present invention to provide analternative manner to desulfating for recovering potassium salts frombrines containing high sulfate concentrations. Another object of theinvention is to selectively and economically recover valuable potassiumsalts from complex solutions. A further object is to selectively,chemically precipitate a potassium salt from complex solutions and toproduce potassium chloride or other salable potassium salts therefrom. Astill further object is to precipitate the potassium salt from solutionwith a reagent that is low in cost and is recoverable with highefliciency. A still further object is to precipitate the potassium saltfrom brines in a form which is readily convertible to highgrade KCl orother salable potassium salts by using lowcost chemicals, preferablychemicals contained in the brines themselves.

Other objects and advantages will be obvious from the detaileddescription of the process appearing in the specification taken inconjunction with the following flow diagram in which the overallpotassium recovery and production procedure is shown.

Potassium-bearing brine or solution I 501mg] K0104 solution NaClOr forreuse gs i ri on exchange potassium resin NaCl, Na2SO4, NaNO; or sodiumresin for reuse NagCO; brine elution potassium solution evaporation K01,K 504, KzCO; or KNOa In accordance with the invention, a complex brinecontaining Na, K, Mg, Cl, and S0 is treated with a solution of NaClOwhereby the potassium is precipitated as KC104. Since the completenessof KClO, precipitation is in part dependent on temperature, it is,therefore, desirable to chill the brine prior to. treatment with NaClO Abrine temperature of from about lO to about 0 C. is preferable. If thebrine is not chilled, NaClO, in excess of stoichiometric requirementswill be required because the KCIO, is fairly soluble in brine, at roomtemperature, in the absence of excess perchlorate. At low brinetemperatures (e.g., 10 to 0 C.) a stoichiometric amount of NaClO,results in high potassium recovery, although an excess is conducive toeven a higher recovery. For a brine containing potassium in the range of15 to 60 grams per liter, recovery of perchlorate and potassium withstoichiometric additions of NaClO; at 10 to 0 C. may be expected torange from about 87 to 97 percent. When using an excess of perchlorate,most of the excess left in the waste brine can be recovered therefromby 1) solvent extraction with a tertiary or quaternary alkyl aminefollowed by stripping with cold, potassium-bearing brine or a solutionof NaCl and Na CO or (2) adsorption of perchlorate from spent brine onanion exchange resins Ifpllowed by elution with fresh, cold,potassium-bearing rine.

Following precipitation of KClO the precipitate is recovered bysettling, filtration, or centrifuging, washed with a small volume ofcold water saturated with KClO and then dissolved in hot water.Solubilities in the order of 140 to 200 grams per liter are obtainablein the temperature range of to 100 C. The hot solution is then passedthrough a loading column containing a bed of the sodium form of a cationexchange resin of the nuclear sulfonic type, moving countercurrent tothe flow of KClO solution. The efiiuent from this operation is asolution of NaC1O substantailly free of potassium and suitable forrecycle to the precipitation step. Under proper operating conditionswith respect to resin and solution flowrates, all of the sodium on theresin is displaced by potassium. Alternatively, an anion exchange resincould be employed whereby the KClO, is directly converted to the desiredsalt solution, but eocnomics and reaction kinetics favor the use ofcation exchange resins.

Following conversion of the resin to the potassium form, the resin istransferred to an elution column in which the resin is movedcontinuously, countercurrent to allow of NaCl brine. Again, under properoperating condltions with respect to NaCl brine concentration, and

brine and resin flowrates, a substantially sodium-free KCl brine isobtained. Efiluent concentrations of up to about 200 grams of KCl perliter with only 1 to 2 grams of NaCl per liter can be achieved. Ifdesired, a solution of Na SO Na CO or NaNO may be substituted for theNaCl brine, in which case the potassium efiiuent is a solution of thecorresponding anion. Hence, whichever salt offers the best market couldbe produced in the same equipment.

Final recovery of the potassium salt is achieved by simple evaporationin multiple effect evaporators, by spray drying, or other suitablemeans.

The following example illustrates the eifectiveness of the process:

Example 1) Fifteen liters of a waste bittern taken from a Great SaltLake processing plant and containing in grams per liter: 16 K, 27 Mg, 80Na, 175 C1, and 60 SO were cooled to 5 C. As a result of chilling, abouthalf the sulfate was precipitated as hydrated sodium sulfate, while thepotassium and magnesium content remained the same. The crystallizedsodium sulfate was removed by filtration and a slightly less thanstoichiometric amount of sodium perchlorate was then added to the boldbittern. The resultant solution was mechanically stirred forapproximately 30 minutes and the potassium perchlorate then allowed tosettle. This latter operation was conducted at low temperaures of aboutto 0 C. The settled potassium perchlorate was subsequently filtered,washed, and dried, and the products of the test were assayed. The barrenbrine contained 2.1 grams of C10; and 3.28 grams of K per literindicating that 80 percent of the potassium had been removed while 6percent of the perchlorate was lost to the brine. These values are ingood agreement with the experimentally determined solubility product ofKCIQ which is about 16x10- mole per liter at 10 C. in a brine of thiscomposition. The KClO precipitate, after Washing and drying, assayed inexcess of 99 percent KClO, and contained only 0.02 percent Na.

(2) The K010 precipitate was dissolved in water at 70 to 80 C. establisha 0.7 M concentration, and was passed through a fixed bed type cationexchange resin bed which had been converted to the sodium by treatmentwith NaCl brine. Saturation loadings of 1.9 to 2.1 equivalents or 75 to85 grams of potassium were consistently obtained. Resin loadings to thefirst appearance of potassium in the efiluent ranged from 20 to 40 gramsper liter, which showed that with multiple, fixed bed ion exchangecolumns or a countercurrent column, a NaClO solution substantially freeof potassium could be produced for recycle on a continuous basis.

(3) Elution of potassium from loaded resin was obtained by passingsolutions of NaCl, Na CO and Na SO, through a fixed bed of loaded resinat temperatures of C. to 75 C. and solution flowrates equivalent toretention times of 10 to 20 minutes. Solution strengths ranged [from 2to 3 M. Sampling of the eluate in small increments showed that dependingupon the influent concentration of NaCl, Na SO or Na CO peakconcentrations of 2 to 3 moles of potassium were obtained, withaccompanying sodium concentrations of only 0.2 to 0.5 gram per liter.There were only minor dilferences in elution efiiciency between NaCl NaCO and Na SO In further tests with a 2 inch diameter by 10 feet highcontinuous countercurrent ion exchange column, resin in the potassiumform was continuously eluted with NaCl solutions of differentconcentrations and yielded efiiuents containing 135 to 190 grams of KCland 5 to 7 grams of NaCl per liter. Evaporation of these solutions andsimple fractional crystallization yielded products containing in excessof 99 percent KC].

In the process of the present invention, by employing sod um perchlorateas the precipitant, reagent costs are marntamed comparatively low andreagent can be easily 4 recovered for reuse. Furthermore, theperchlorate possesses a high selectivity for potassium and forms asubstantially insoluble salt therewith in cold brines. However, the keyto the use of perchlorate is the comparatively easy conversion of asolution of KClO to NaC1O by ion exchange.

Although the particular process is well adapted to carry out the objectsof the present invention, it is to be understood that variousmodifications and changes may be made all coming within the scope of thefollowing claims.

What is claimed is:

1. A process for producing a potassium salt product from a potassiumsalt-bearing solution, said potassium salt product selected from thegroup consisting of potassium chloride, sulfate, carbonate and nitrate,comprising (a) adding NaClO, to said solution in suflicient quantity toprecipitate potassium from said solution as K0104;

(b) separating said KClO precipitate from remaining solution and forminga KClO, solution;

(c) ion exchanging the potassium ion of said KClO solution with sodiumion by means of an ion exchange resin to separate potassium ion fromperchlorate ion; and

(d) combining said potassium ion with an anion selected from the groupconsisting of chloride, sulfate, carbonate and nitrate by ion exchange.

2. The process of claim 1 wherein said potassium-bearing salt solutionis maintained in a chilled condition during said precipitation step.

3. The process of claim 2 wherein said salt solution is maintained at atemperature of about 10 to about 0 C. during said precipitation step.

4. The process of claim 1 wherein said ion exchange resin is the sodiumform of a cation exchange resin whereby said step (c) regenerates saidresin to the potassium form, and wherein said step (d) of combining saidpotassium ion with said anion comprises eluting said p0.- tassium fromsaid potassium form of said resin with a sodium salt solution containingsaid anion.

5. The process of claim 4 wherein said potassiumbearing salt solution ismaintained at a temperature of about 10 to about 0 C. during saidprecipitation step.

6. The process of claim 4 wherein sodium perchlorate formed during saidion exchange is employed in said precipitation step.

7. The process of claim 6 wherein the sodium form of said ion exchangeresin formed during said elution step is employed in said ion exchangestep.

8. The process of claim 7 wherein said potassium-bearing salt solutionis selected from the group consisting of a brine and a bittern andwherein said brine or bittern is maintained at a temperature of about 10to about 0 C. during said precipitation step.

9. The process of claim 8 wherein the potassium salt solution formedduring said elution step is evaporated to dryness to form a solidpotassium salt.

References Cited UNITED STATES PATENTS 1,338,235 4/1920 Mcllhiney 23-391,716,663 6/1929 Pike et al 23-38 2,619,404 11/1952 Skogseid 23-38 X2,900,223 8/ 1959 Cunningham 23-63 3,078,140 2/ 1963 Hatch 23-89 X3,096,153 7/1963 Hadzeriga 23-121 OSCAR R. VERTIZ, Primary Examiner.

G. T. OZAKI, Assistant Examiner.

US. Cl. X.R.

